Cargo transported by aircraft is-generally loaded onto pallets or into containers having set dimensions, and termed unit load devices (ULDs). There are two standard sizes of ULDs, both of which have 125-inch (3175 mm) lengths. The 88-inch units have a width of 2235 mm and the 96-inch units have a width of 2438 mm. ULDs are loaded through a cargo door in the side of the aircraft onto a floor of a cargo compartment.
The floor of the cargo compartment is provided with devices for facilitating movement of the ULD during loading and unloading operations. A plethora of freely rotating conveyance roller-balls protrude through the floor to provide low friction support for the ULDs. Power drive units (PDUs) are energiseable to be elevated from beneath the floor to a level just above the conveyance rollers. Each PDU is a separate electro-mechanical actuator which includes one or more rubber coated wheels or drive rollers for contacting the underside of the ULD and providing a drive to move the ULD in a set direction.
In a known cargo compartment, the compartment is just wide enough for the ULDs to fit length-wise across the compartment. Lateral PDUs are provided to drive the ULD through the door in the aircraft side until it is situated entirely within the compartment. Longitudinal PDUs are then energised to drive the ULD along the compartment to its final position. The cargo is loaded through a 98-inch door, which has an opening about 50 mm larger than the width of the wider, 96-inch ULDs.
By narrowing the width of the cargo compartment at a point between the cargo door and the farther end of the compartment, better use can be made of the space in an aircraft. To make use of this space, however, it is necessary to turn the ULDs before they are driven into position in the narrower portion of the compartment. This presents a difficulty as the close fit between the width of the ULD and the cargo door opening restricts the room available for turning. Also, the orientation of the PDUs is such as to drive the ULD in either a lateral or longitudinal direction, but not to facilitate turning.
U.S. Pat. No. 5,101,960 describes a cargo loading system for an aircraft, in which the ULDs are turned about a pivot device as the ULD is loaded into the cargo compartment. The pivot device has a normal position below the conveyance plane, in which it is out of contact with the ULD, and is moved towards frictional engagement with the ULD so as to form a pivot axis when the ULD is to be turned. Rotating conveyance rollerballs drive the ULD, which is pinned at the pivot axis, such that the ULD is pivoted. When the desired rotation is achieved the pivot device is lowered so that the ULD may be fully conveyed into the compartment. One problem with this system is that the rubber coated wheels or drive rollers, which contact the underside of the ULD, are prone to scrubbing and side loading which adversely affect tyre life. Additionally, the system is not compatible with all types of aircraft compartment as a large overhang space is required for the ULD during turning.
It is an object of the present invention to remove or alleviate at least one of the aforementioned problems.